<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
#one {
    width: 100px;
    height: 100px;
    background: lightblue;;
}

    </style>
</head>
<body>
    <select name="" id="select">
        <option value="2">2</option>
        <option value="3">3</option>
        <option value="4">4</option>
    </select>


      <div id="one">111</div>
    <script>

        // click
        // dbclick
        // mouseuover
        // mouserout
        // change 
        document.getElementById("one").onkeydown = function() {
            alert(1)
        }
        document.getElementById("one").onmouseout = function() {
            alert(1)
        }



       let el = document.getElementById('select');
       el.onchange = function() {
         let index = el.selectedIndex
        //  debugger
         let value =   el.options[index].value
           console.log(value);

       }
    </script>
</body>
</html>